1. Field of Invention
The present invention relates to devices for detecting radiation, particularly to devices for determining skin-damaging levels of ultraviolet (UV) radiation.
2. Description of Prior Art
Solar radiation reaching the earth consists of electromagnetic energy ranging from ultraviolet (UV) light to infrared (IR) light. UV radiation is further subdivided into three types: UV-A, UV-B, and UV-C. UV-C radiation has wavelengths in the range of 200 to 285 nanometers (nm) and is totally absorbed by the earth's atmosphere. UV-B, ranging from about 285 to 318 nm, is known to cause skin cancer in humans. UV-A, from about 315 to 400 nm, is mostly responsible for tanning the skin. However, UV-A has also been found to play some role in skin cancer and is the cause of eye cataracts, solar retinitis, and corneal dystrophies.
Based on general principles and techniques for radiometry and photometry, several UV radiation-measuring and warning instruments have been developed and made commercially available.
A personal UV radiometer, described in U.S. Pat. No. 5,008,548 to Nahum Gat, 1991, includes an LCD display, a photocell, and an integrated circuit for processing subject inputs and UV radiation data.
However, this radiometer is unable to correctly monitor levels of UV radiation when it is not directly exposed to solar rays, i.e., when it is placed in the shade. Moreover, the device does not take into account the changes in skin pigmentation which occur while a person is being exposed to solar radiation. Furthermore, this device is not optimally convenient, since it is intended to be attached to an article of clothing and may restrict the movement of a person during vigorous physical activity, for instance, a volleyball game.
Another apparatus, disclosed in U.S. Pat. No. 4,985,632 to Frank Bianco et al., 1991, comprises an electronic wristwatch having a digital readout for displaying the time, the day, and the month. It also incorporates a photodiode for detecting skin-damaging UV radiation, a microcomputer, and four function buttons.
This device, however, is not subject-friendly due to its large number of functions, many of which are superfluous. Moreover, like the radiometer, the wristwatch does not take into account skin pigmentation changes which occur during exposure to UV radiation. Furthermore, it can not monitor UV radiation when placed in the shade.
All of the above cited prior-art devices are based on the assumption that the amount of UV radiation that may be safely tolerated by human skin is independent of the intensity of incident radiation and is determined only by the total accumulated energy. Even though some prior-art devices directly measure the intensity level of incident radiation, this measurement is not factored into the calculation of a safe UV energy threshold.
The applicants propose to solve this problem by providing a noseshade for monitoring exposure to UV radiation by separately measuring UV-A and UV-B radiation doses (U.S. Pat. No. 5,151,600 issued Sep. 29, 1992 to M. Black). The UV radiation control system of the nosepiece incorporates a pair of photodetectors with appropriate narrow-band pass optical filters for transmitting the UV-A and UV-B spectral components, respectively. The outputs of these photodetectors are connected to an integrated central processor unit (CPU). The output of the CPU, in turn, is connected to an indicator, such as a piezoelectric element which produces an audible signal when the daily threshold dose of UV-A radiation is exceeded.
Although such a device may provide a reliable indication of overexposure, it has a number of disadvantages which are the following: 1) it is not a common practice to wear nosepieces because people feel conspicuous covering their noses and are embarrassed to wearing such nosegear; 2) the audible warning signal is not always heard by the wearer, especially when the wearer of the nosepiece in on a noisy beach.